Bottom construction of ponds particularly solar ponds

Abstract

A pond construction, especially useful for non-convective solar ponds, having a multi-layer bottom in order to minimize seepage of liquid through the pond bottom. Liquid which permeates the multi-layer construction is pumped back into the pond.

What is claimed is: 
     
       1. A pond containing a body of liquid, characterized in that, in order to minimize seepage of the liquid through the pond bottom, the pond comprises a multi-layer bottom construction over the natural earth and underlying the complete pond, which bottom construction includes an upper layer of a permeable material having a low degree of permeability to the liquid in the pond, an intermediate layer of a permeable material having a high degree of permeability to the liquid in the pond, and a bottom layer of a permeable material having a low degree of permeability to the liquid in the pond; and pumping means for returning the liquid which permeates through the upper layer into the intermediate layer, back to the pond above the upper layer. 
     
     
       2. A pond according to claim 1, wherein the pond is a thermal pond containing a heated liquid. 
     
     
       3. A pond according to claim 2, wherein the pond is a non-convective solar pond containing a body of liquid to be heated by solar radiations. 
     
     
       4. A pond according to claim 1, wherein said pumping means comprises drainage piping located in said intermediate layer for receiving the liquid permeating through the upper layer, return piping communicating with the bottom of the pond above the upper layer, and a pump for pumping said permeating liquid from the drainage piping through the return piping back to the bottom of the pond above the upper layer. 
     
     
       5. A pond according to claim 4, wherein said pump is located in a sump receiving liquid drained via the drainage piping. 
     
     
       6. A pond according to claim 5, wherein said sump is vented to the atmosphere to remove gases evolved below the bottom of the pond and passed therefrom to the sump before return of the drained liquid back to the bottom of the pond. 
     
     
       7. A pond according to claim 1, wherein said pumping means is located laterally of the pond and includes a liquid level detector for automatically actuating the pumping means when the drained liquid in the sump exceeds a predetermined high level and for automatically stopping the pumping means when the drained liquid drops below a predetermined low level. 
     
     
       8. A pond according to claim 1, wherein the impermeable upper layer has a thickness less than that of the permeable intermediate layer, and wherein the latter layer has a thickness less than that of the impermeable lower layer. 
     
     
       9. A pond according to claim 1, wherein the upper and lower layers have a permeability of about 10 -5  to 10 -6  cm/sec. 
     
     
       10. A pond according to claim 1, wherein said drainage piping comprises a plurality of transversely extending drainage pipes spaced longitudinally of the pond and joined to a further collection pipe extending longitudinally of the pond and leading to said sump.